1. Field of the Invention
The present invention relates to a method for forming a metal line having an Al/Cu structure, and more particularly, to a method for forming a metal line having an Al/Cu structure in which a metal line having a layered structure of a first Ti/TiN layer, an Al layer, a third Ti/TiN layer and a Cu layer is formed to improve the integration density, the manufacturing yield and reliability of the resulting semiconductor devices.
2. Background of the Related Art
A conventional method for forming a metal line will be described with reference to FIGS. 1A to 1C.
As shown in FIG. 1A, a first Ti/TiN layer 13, an Al alloy layer 15, and a second Ti/TiN layer 17 are sequentially formed on an insulating substrate 11 having a metal line contact hole (not shown).
As shown in FIG. 1B, a photoresist film is deposited on the second Ti/TiN layer 17. The photoresist film is then selectively exposed and developed by a positive patterning process to form a photoresist pattern 19 protecting those portions where metal lines will be formed.
As shown in FIG. 1C, the second Ti/TiN layer 17, the Al alloy layer 15, and the first Ti/TiN layer 13 are selectively etched using the photoresist pattern 19 as a mask, so that metal lines having a layered structure of Ti/TiN/Al/Ti/TiN are formed. The photoresist pattern 19 is then removed.
As integration density increases, the distance between adjacent metal lines becomes exceedingly small.
The metal line thickness has increased in order to form the metal line having high resistance to electro-migration and a low electrical resistance value.
As the thickness of the metal line increases, the thickness of photoresist pattern 19 also has to be increased to serve as a mask during the process of forming the metal line.
However, this conventional method for forming a metal line has several problems.
In this conventional method for forming a metal line, since a metal line is formed by etching Ti/TiN/Al/Ti/TiN layer using the photoresist pattern which is formed by the positive patterning process as a mask, the thickness of the photoresist film increases as thickness of the metal line increases due to high integration density of the device. Accordingly, it is difficult to perform the necessary micro-patterning process during the process of forming the photoresist film pattern and the yield and reliability of the resulting devices are degraded.
Accordingly, the present invention is directed to a method for forming a metal line having an Al/Cu structure that substantially overcomes one or more problems resulting from limitations and disadvantages of the prior art.
An object of the present invention is to provide a method for forming a metal line having an Al/Cu structure, in which the metal line is formed with a high resistance to electro-migration and a low electrical resistance value without increasing the thickness of the photoresist film.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a method for forming a metal line having an Al/Cu structure according to the present invention includes the steps of: sequentially forming a first buffer layer, a first metal layer, and a second buffer layer on an insulating substrate; depositing a photoresist film on the second buffer layer at a thin thickness that can be used as a mask to etch the first metal layer to an intermediate depth; forming a photoresist film pattern by removing the photoresist film in a region where the metal line will be formed; forming grooves by selectively etching the second buffer layer and the first metal layer using the photoresist film pattern as a mask and removing the photoresist film pattern; forming a third buffer layer on an entire surface; filling the grooves with a second metal layer having a lower electrical resistance and a higher resistance to electro-migration than the first metal layer; entirely etching the second metal layer and the third buffer layer on the second buffer layer; and forming a metal line having a layered structure of the first buffer layer, the first metal layer, the third buffer layer, and the second metal layer by selectively etching the third buffer layer, the second buffer layer, the first metal layer, and the first buffer layer using the second metal layer as a mask.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.